Pressurized sump



April 28, 1964 v, HUNT 3,130,548

PRESSURIZED SUMP Filed Dec. 22, 1961 INVENTOR VICTOR F. HUNT I y zwm ATTORNEY United States Patent 3,139,548 PRESSURHZED SUW Victor F. Hunt, Battle Creek, Mich, assignor to Clark Equipment (Jornpany, a corporation of Michigan Filed Dec. 22, 1961, Ser. No. 161,698 13 Claims. (Cl. 60-52) This invention relates to a hydraulic system and particularly to a hydraulic system in which the sump or reservoir is pressurized in a novel manner during operation.

Previously in the field of hydraulic power systems problems have been encountered which relate to the supply of a sufiicient volume of hydraulic fluid to the inlet side of the pump so that the pump is capable of generating its rated output. For example, pump performance in hydraulic systems is frequently seriously aflected if the pump is located at a higher level in the system than the oil level in the sump, or if the conduits of the system have numerous ends or other restrictions which tend to limit the capacity of the pump below its rated capacity because of inadequate fluid supply at the pump inlet.

The present invention comprises a simple and economic hydraulic system arrangement which facilitates the automatic pressurizing of sumps and reservoirs so that the pressure supply pump is always assured of adequate inlet conditions which facilitates operation of the pump at maximum volumetric efilciency.

It is therefore a primary object of the present invention to provide an improved hydraulic system in which the fluid supply to the inlet side of the pump is automatically pressurized during operation of the system.

Another object of the invention is to provide a sump or reservoir pressurizing means in hydraulic systems which operates as an inherent part of such systems.

A further object of the invention is to provide in a hydraulic system check valve means which controls the supply of pressurized air to a reservoir in the system, said pressurized air being supplied by system motor means which is activated by pump means which in turn receives hydraulic fluid supply from the reservoir.

Other objects and advantages of the invention will become apparent to persons skilled in the art following a de tailed description of the single figure which illustrates a hydraulic system embodying my invention.

Referring now in detail to the drawing, a single acting piston and cylinder asesmbly, such as is used in industrial lift trucks, is illustrated at numeral and is of the wellknown type which includes a cylinder 12, a gland 14, a piston head 16, and a piston rod 18 extending through cylinder chamber 19 and the gland 14. End 21) of the piston rod is adapted to be connected to any suitable mechanism. A dual oil and air sump 22 and 24 is connected together by a conduit 26, the oil sump being connected to the liquid chamber 27 of cylinder 12 by way of a pump inlet conduit 28, a gear pump 30, a pump discharge conduit 32, a conventional manual selector valve 34, and a conduit 36. A by-pass port in the selector valve is connected by a conduit 38 to the lower portion of sump section 22. Air chamber 19 of cylinder 12 is connected to the upper end of sump section 22 by way of an air conduit 40, a one-way check valve 42 and a conduit 44. Vent conduit 40 is connected to the atmosphere by way of an air filter 46 and a one-way check valve 48 as shown. A pressure relief valve 519 is connected to sump section 24.

In operation, gear pump 30, which may be continuously driven from an engine power take-01f or other suitable motive means, normally circulates oil from sump 22 through line 28 and back to the sump through valve 34 and return line 58 when the selector valve is in a neutral position, thus maintaining constant the oil level in sump 22. It should be pointed out that air sump section 3,l3,548 Patented Apr. 28, 1964 24 is preferably prepressurized and tends to maintain the upper air portion of sump 22 under pressure through conduit 26. Valve 34 may be manually positioned by means of lever 52 to direct the output of pump 34 to high pressure conduit 36, thus pressurizing chamber 27 of cylinder 12 and actuating piston 16 outwardly of the cylinder to lift a load or perform other work. Such movement of piston 16 forces the air from chamber 19 of the cylinder through conduit 40, one-way check valve 42 and conduit 44 into the upper end of sump 22 and into sump 24 through conduit 26 to maintain pressure on the oil, and thus assure a supply of pressurized oil to the inlet side of pump 30 so that the pump is not starved during operation. When lever 52 is actuated to a second operating position conduit 36 is vented through the valve to return line 33 and piston 16 retracts within the cylinder under gravity load, for example, to force the fluid therefrom back to the sump, thus increasing the oil level therein and transmitting pressurized air to sump section 24. Relief valve opens to relieve air pressure in the sump above a predetermined amount. During downward movement of piston 16 chamber 19 tends to become evacuated which causes one-way check valve 43 to open and allow atmospheric air to enter chamber 19 through air filter 46, the check valve and conduit 40. Such air volume is prevented from entering the sump since the air pressure therein maintains check valve 42 closed, and the chamber 19 is replenished with clean air at atmospheric pressure due to the action of the check valves and filter 46.

The above-described cycle may be repeated indefinitely; clean filtered air is provided at all times in the system. The supply of continuous air pressure in the sump in accordance with my invention greatly facilitates the eflicient operation of hydraulic pumps under adverse conditions.

Although only one embodiment of the invention has been disclosed, it will be evident that modifications and rearrangements of the hydraulic system may be made within the scope of the invention. For example, the oil and air sumps could readily be combined in one reservoir with the oil maintained at a level to allow suflicient air space above it. The invention is particularly advantageous when pumps are located above the supply reser voir therefor.

I claim:

1. A hydraulic system comprising single acting motor means having a normally closed air space therein, a liquid reservoir having a normally closed air space associated therewith, pump means for directing pressure liquid from said reservoir to said motor means, conduit means connecting the air space in said motor means to the air space of said reservoir, check valve means permitting a flow of pressure air to the latter air space through said conduit during actuation of said motor means in one direction, and additional check valve means permitting a flow of atmospheric air to the air space in said motor means during actuation of said motor means in the opposite direction.

2. A hydraulic system comprising motor means having a piston, a normally closed air chamber on one side of the piston and a liquid chamber on the other side thereof, a closed liquid reservoir having an air space associated therewith, pump means for directing pressure liquid from said reservoir to the liquid chamber in said motor means, conduit means connecting the air chamber in said motor means to the air space of said reservoir, and one-way check valve means permitting a flow of pressure air from said air chamber to said air space through said conduit for maintaining the liquid in said reservoir under superatmospheric pressure during actuation of said motor means in a direction which increases the volume of the liquid chamber and decreases the volume of the air chamber thereof.

3. A hydraulic system as claimed in claim 2 wherein second check valve means is connected to said air chamber for providing air flow thereto during a reversal of movement of said motor means wherein the volume of said liquid chamber decreases while the volume of said 'air chamber increases.

4. A hydraulic system as claimed in claim 3 wherein filter means is provided in series with said second check valve means for providing clean air to said air chamber.

5 A hydraulic system comprising extensible and retractable motor means having a reciprocable piston and fluid and liquid chambers on the opposite sides of the piston normally closed to the fluid atmosphere surrounding the hydraulic system, a liquid reservoir having a fluid space associated therewith for maintaining pressure on the liquid in said reservor, pump means having an effective elevation relative to the liquid level in said reservoir for directing pressure liquid from said reservoir to the liquid chamber in said motor means, conduit means connecting the fluid chamber in said motor means to the fluid space in said reservoir, and one-way valve means permitting a flow of pressure fluid only through said conduit to the fluid space in said reservoir during actuation of said motor means in a direction to decrease the volume of said fluid chamber.

6. A hydraulic system as claimed in claim 5 wherein second one-way valve means is provided upstream of said first one-way valve means for providing a flow of fluid to said fluid chamber during actuation of said motor means in a direction to increase the volume of said fluid chamber.

7. A hydraulic system comprising a motor means having a piston and normally closed fluid and liquid chambers on opposite sides of the piston, a normally closed liquid reservoir having a fluid space associated therewith for maintaining pressure at all times on the liquid in the reservoir, pump means for generating a flow of pressure liquid from said reservoir to said liquid chamber whereby to decrease the volume of said fluid chamber, conduit means connecting said fluid chamber to said fluid space, and valve means directing a flow of super-atmospheric pressure fluid through said conduit means from said fluid chamber to said fluid space only during such movement of said motor means.

8. A hydraulic system as claimed in claim 7 wherein additional valve means is provided for directing the flow of additional fluid only to said fluid chamber during movement of said motor means in an opposite direction.

9. A hydraulic system as claimed in claim 7 wherein relief valve means is connected to said fluid space for exhausting fluid pressure therefrom above a predetermined value.

10. A hydraulic system as claimed in claim 7 wherein said pump means has an effective elevation above the level of liquid in said reservoir.

11. A hydraulic system comprising motor means having a piston and a normally closed variable volume air chamber on one side and a closed variable volume liquid chamber on the other side of the piston, a liquid contain ing reservoir having a pressurized air space above the liquid level, conduit means communicating the liquid in vsaid reservoir to said liquid chamber, pump means in said conduit means for directing pressurized fluid to said liquid chamber whereby to actuate said motor means to decrease the volume of said air chamber, conduit means connecting said air chamber to said air space, first check valve means in said conduit means permitting a flow of pressurized air to said air space only during movement of said motor means to decrease the Volume of said air chamber, other conduit means connected to the first conduit means intermediate said air chamber and said check valve means, and second check valve means in said second conduit means for directing a flow of air through said first and second conduit means to said air chamber only during actuation of said motor means in a direction to increase the volume of said air chamber.

12. A hydraulic system as claimed in claim 11 wherein filter means is provided in one of said conduits for providpressurized air to said air space whereby to maintain proper and adequate liquid pressure at the inlet to said pump and an air supply to said air chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,644,101 Anderson Oct. 4, 1927 1,714,528 Staggs May 28, 1929 2,575,241 White Nov. 13, 1951 2,972,863 Hyde Feb. 28, 1961 

1. A HYDRAULIC SYSTEM COMPRISING SINGLE ACTING MOTOR MEANS HAVING A NORMALLY CLOSED AIR SPACE THEREIN, A LIQUID RESERVOIR HAVING A NORMALLY CLOSED AIR SPACE ASSOCIATED THEREWITH, PUMP MEANS FOR DIRECTING PRESSURE LIQUID FROM SAID RESERVOIR TO SAID MOTOR MEANS, CONDUIT MEANS CONNECTING THE AIR SPACE IN SAID MOTOR MEANS TO THE AIR SPACE OF SAID RESERVOIR, CHECK VALVE MEANS PERMITTING A FLOW OF PRESSURE AIR TO THE LATTER AIR SPACE THROUGH SAID CONDUIT DURING ACTUATION OF SAID MOTOR MEANS IN ONE DIRECTION, AND ADDITIONAL CHECK VALVE MEANS PERMITTING A FLOW OF ATMOSPHERIC AIR TO THE AIR SPACE IN SAID MOTOR MEANS DURING ACTUATION OF SAID MOTOR MEANS IN THE OPPOSITE DIRECTION. 